Since an electroluminescent element utilizing electroluminescence of an organic compound has high visibility due to being self-luminous, and has characteristics such as a low driving voltage, the use as a light-emitting device has attracted attention in various display devices.
Further, particularly in order to expand applications of the aforementioned electroluminescent device, a multicolor application such as an area-color or full-color display (hereinafter, referred to as “a multicolor display device”) is expected.
As methods of manufacturing a multicolor display device using an electroluminescent device, the following methods are known:
(1) A method of arranging EL materials emit in three primary colors of red (R), green (G), blue (B) in a matrix (Refer to Japanese Patent Laid-Open No. 57-157487, Japanese Patent Laid-Open No. 58-147989, and Japanese Patent Laid-Open No. 3-214593, for example.).
(2) A method of taking out three primary colors of RGB, where an EL device that emits in white is combined with a color filter (Refer to Japanese Patent Laid-Open No. 1-315988 and Japanese Patent Laid-Open No. 2-273496, for example.).
(3) A method of converting into three primary colors of RGB, where an EL device that emits in blue is combined with a color-changing fluorescent film (Refer to Japanese Patent Laid-Open No. 3-152897, for example).
(4) Further, a technique of making a conductive polymer material that is used for an electroluminescent device into ink to perform patterning of an EL material by an ink-jet method is known as a method of manufacturing a multicolor display device without forming a color filter or a fluorescence conversion filter required for the aforementioned method (2) or (3) (Japanese Patent Laid-Open No. 10-153967 and Japanese Patent Laid-Open No. 11-87062, for example).
However, a group of π-conjugated polymers that have been researched long as conductive polymer materials in terms of advantages such as stability have rigid main chains, and are often insoluble or non-melted generally, which therefore cannot be used in the aforementioned ink-jet method. Consequently, for the use in the ink-jet method, a chemical contrivance (such as introduction of a substituent) for solubilizing the conductive polymer materials is required. However, in the case of being solubilized, there is a problem such as lowering of a charge transport property or thermal stability. Further, In the case of forming the conductive polymer materials by the ink-jet method as a hole injection layer, advanced techniques are required in order to prevent an electric leak between respective pixels (crosstalk).
Besides, as another method of manufacturing an electroluminescent device, electrochemical methods have been proposed. As one of the electrochemical methods, electrolytic polymerization is known, which is a method in which at least one of an anode electrode and a cathode electrode opposed mutually is dipped in an electrolytic solution (a polymerization solution) including a material for forming a hole transport layer or an electron transport layer, and then, the hole transport layer or the electron transport layer is formed on the dipped anode electrode or cathode electrode to be covered by applying a voltage between the anode electrode and the cathode electrode. In manufacturing of an electroluminescent device by electrolytic polymerization, a conjugated polymer material that is superior in an injection of a hole or an electron and a charge transport performance and also has high stability thermally can be used (Refer to Japanese Patent Laid-Open 9-976979, for example.). However, an organic material for forming a light-emitting layer by an electrochemical method is not mentioned at all in Japanese Patent Laid-Open 9-976979.